The present invention relates to the field of manufacturing construction products, and, more particularly, to methods for making lightweight, high-strength, fire-resistant wallboard sheet, and/or moisture-resistant backerboard sheets.
Wallboard sheets are widely used in building construction to form partitions or walls of rooms, elevator shafts, stair wells, ceilings, etc. The sheets are typically fastened to a suitable supporting framework. The seams between sheets are covered to provide an even wall surface. The sheets may be readily cut to size by first scoring the face sheet, and then snapping the board about the score line. The wall may then be painted or covered with a decorative wall covering, if desired. Such wallboard sheets created from a gypsum core with outer face layers of paper, sometimes referred to as gypsum board or drywall, are well known.
Gypsum wallboard is typically manufactured by delivering a slurry or paste containing crushed gypsum rock onto a moving sheet of facing paper to which a second or top paper layer is then added to form a long board line. The board line permits the slurry to harden before being cut. The cut panels are heated in a kiln, before being packaged for storage and shipping.
Typically, such sheets are xc2xd or ⅝ inch thick and in conventional sizes of 4xc3x978 feet, such a gypsum wallboard sheet may weigh about 55-70 pounds. Accordingly, handling of such gypsum wallboards presents a significant task for construction personnel or wallboard xe2x80x9changersxe2x80x9d, particularly when such boards are secured overhead to form a ceiling. In addition, the fire resistance, thermal insulation and sound absorbing properties of conventional gypsum wallboard sheets may not be sufficient for some applications.
Another variation of gypsum wallboard is water-resistant drywall or xe2x80x9cgreenboardxe2x80x9d. The greenboard typically includes the same gypsum core, but includes a water-resistant facing so the water is less likely to penetrate, stain and/or decay the wall. Greenboard is typically used for walls in a moist or humid environment, such as a bathroom, for example. Such greenboard is not typically recommended as an underlayment for tile in the bathroom, for example, since water may penetrate the grout or cracks between adjacent tiles and deteriorate the greenboard. U.S. Pat. No. 5,552,187 to Green et al. discloses the addition of a fibrous mat-faced gypsum board coated with a water-resistant resinous coating for greater durability in moist environments.
Yet another related conventional wallboard product to serve as an underlayment for wet areas is the concrete backerboard. For example, UTIL-A-CRETE(copyright) Backerboard from Bonsal is a precast cementitious backboard with glass mesh reinformcement. The board includes portland cement, fiber glass mesh and lightweight aggregate. The backerboard is more adapted to be used in areas subject to splashing or high moisture.
While the glass mesh face layers are typically secured to the surface of the backerboard after the core has been precast, continuous production is also disclosed in U.S. Pat. No. 5,221,386 to Ensminger et al. In addition, the mesh or reinforcing layers have also been embedded in the faces and edges of the backerboards.
Unfortunately, conventional cementitious backerboards may be more difficult to score and break to size. Moreover, since the backerboards include a core of cement, their density is considerably greater than even conventional gypsum wallboard. Accordingly, manufacturers may offer the backerboards in smaller sizes to be more readily handled by the installer, but such increases seams between sheets and also increases costs of installation. A typically-sized 4 foot by 8 foot sheet can weigh well over 100 pounds, which is very unwieldy especially in confined spaces.
In view of the foregoing background, it is therefore an object of the invention to provide a method for making wallboard or backerboard sheets which are relatively lightweight, strong, and which have good fire resistance, thermal insulation, and sound absorbing properties.
This and other objects, features and advantages in accordance with the present invention are provided by a method comprising forming core material having opposing first and second major surfaces and comprising aerated concrete, securing at least one face layer on at least one of the first and second major surfaces of the core material, and cutting the core material and at least one face layer secured thereto into a plurality of wallboard or backerboard sheets. The provision of aerated concrete for the core provides many key advantages over conventional gypsum wallboard sheets, and/or conventional backerboard sheets, such as gypsum greenboard or cementitious backerboard, for example.
In one class of embodiments, the method may further comprise curing the core material prior to securing the at least one face layer thereto. In another class, the method may further comprise curing the core material after securing the at least one face layer thereto.
In one particularly advantageous embodiment, forming the core material comprises dispensing materials for making aerated concrete into a mold and allowing the materials to rise and stiffen into a body, curing the body, and dividing the cured body into a plurality of cured sheets to serve as the core material. The plurality of the cured sheets may be joined together in end-to-end relation while advancing the cured sheets along a path of travel. In addition, securing the at least one face layer may be performed while the cured sheets are advanced along the path of travel.
In another embodiment, forming the core material comprises dispensing materials for making aerated concrete into a mold and allowing the materials to rise and stiffen into a body, dividing the body into a plurality of uncured sheets, and curing the sheets to serve as the core material. This embodiment may also include joining the plurality of the cured sheets together in end-to-end relation while advancing the cured sheets along a path of travel. Additionally, the at least one face layer may also be secured while the cured sheets are advanced along the path of travel.
In yet another embodiment, forming the core material comprises dispensing materials for making aerated concrete into a mold and allowing the materials to rise and stiffen into a body, and dividing the body into a plurality of uncured sheets to serve as the core material. In this embodiment, curing of the uncured sheets occurs after securing the at least one face layer thereto. Curing may also be performed after cutting. A high temperature resistant face layer may be required where curing is performed after securing of the one or more face layers.
In accordance with still another embodiment of the invention, the method includes mixing and dispensing the materials for making aerated concrete in slurry form, and wherein securing the at least one face layer comprises receiving the aerated concrete in slurry form thereon as the at least one face layer is advanced along a path of travel. This embodiment may also include permitting the aerated concrete material to rise and stiffen, and curing the liquid aerated concrete after rising and stiffening. The curing may also be after cutting.
The securing the at least one face layer may comprise securing first and second face layers on respective first and second major surfaces of the core material. The at least one face layer may comprise paper, such as for a wallboard. Alternately, the at least one face layer may be moisture-resistant for a backerboard.
The method may also include forming the first major surface of the core material to have beveled portions adjacent respective opposing longitudinal side edges. Securing the at least one face layer may include securing the at least one face layer to extend around the opposing longitudinal side edges. In addition, forming the core material may comprise forming the core material with reinforcing fibers in the aerated concrete.